The present invention relates to a loader and particularly to the types of mobile loaders that incorporate at least one variable height platform, such as are used for loading and unloading freight in the cargo holds of aircraft. Still more particularly, in accordance with one aspect of the invention, the present invention relates to a cargo loader platform having a deck that includes an improved array of friction reducing drivable roller assemblies that cause longitudinal and lateral movement of pallets and containers. In accordance with another aspect of this invention, it relates to a loader of this type having an improved arrangement of cylindrical rollers on the sides and end of the container deck which facilitates movement of cargo onto the deck.
Mobile loaders are essential equipment for the loading and unloading of containerized or palletized cargo into and from the holds of aircraft. Such loaders often employ two platforms. One platform, usually referred to as the bridge, provides an interface with the sill of cargo door. The bridge is supported on a hydraulic lift, which provides a high degree of control and stability and allows the height of the bridge to be adjusted to correspond to the height of the aircraft cargo door. Once the bridge is positioned, it typically remains in a substantially constant position with respect to the aircraft, although it is known to make slight adjustments to the height of the bridge to compensate for shifts in the height of the aircraft cargo door as the plane is loaded or unloaded. Although the balance of the following discussion is presented in terms of a loading process, in which cargo is placed onto an aircraft, it will be understood all concepts apply equally to unloading processes.
The second platform, cycles up and down during the loading process, delivering cargo to the bridge. The platform is typically raised and lowered by means of hydraulic systems acting through appropriate mechanical linkages which ensure that the platform maintains a substantially horizontal attitude. For example, a pair of chains powered by hydraulic cylinders cooperate with a platform squaring or stabilizing scissors to ensure that the platform moves vertically during raising and lowering.
The decks of the platform and bridge sections of cargo loaders are typically provided with some type of rollers or other friction-reducing device, so that containers and pallets can be easily slidably moved across the deck and/or re-oriented. In addition, the decks are provided with some type of drive device for imparting motive force to containers and/or pallets. As used hereinafter, both closed containers with relatively rigid bases and pallets having relatively flexible bases with loads of cargo secured thereto are referred to in a generic sense as cargo containing xe2x80x9cobjectsxe2x80x9d.
Because of the nature of the loading process, which may entail lateral, longitudinal and rotational movement, the friction reducing devices on the deck surface must rotate in whichever direction is required to achieve the desired movement, or at least not impede the desired movement. Thus, suitable friction reducing devices can be casters, rollers, wheels, or some combination thereof, and can be actuable in and out of engagement with the underside(s) of the cargo. Similarly, suitable drive devices include motor driven rollers, belts or wheels and can also be actuable in and out of engagement with the underside(s) of the cargo containing objects.
As aircraft and cargo containers have grown in size, it has become increasingly difficult to carry out the loading and unloading of aircraft. First, the sheer size and mass of containers up to 40 feet long and weighing up to 120,000 pounds make handling formidable. In addition, containers are often shaped to correspond to a particular position or orientation within the cylindrical hull of the aircraft. In order to take advantage of this conformity, it is necessary that each container by correctly oriented as it enters the cargo bay. It is often the case, however, that as the containers are delivered to the aircraft cargo loader, they are not oriented correctly. Hence, it is often desired to re-orient a container prior to loading it on the aircraft. In addition, of course, it is necessary to shift the container longitudinally or laterally during the loading process. It will be understood that the concepts disclosed herein with respect to a loading process have equal applicability to unloading and other cargo-handling processes. Because loading is often performed under rigid time constraints, it is desirable that all loading and reorientation steps occur at the fastest possible rate.
Prior art systems have been disclosed that attempt to provide a safe, controlled and effective mechanism for quickly performing the desired handling steps. These typically entail rollers or belts that are actuable in combination, such as those disclosed in U.S. Pat. Nos. 3,944,096 and 4,978,272. It has been found, however, that prior art systems are limited in the size of container that they can maneuver and in the range of handling stems that they can perform. It is therefore desired to provide a cargo loader that is capable of quickly, effectively and safe handling and re-orienting containers over a range of container types and sizes.
It is also known to provide rotatable cylindrical rollers on the outer sides of platform of this type in an effort to compensate for disparity in height between the platform deck and the bed of the truck from which the cargo is to be loaded onto the platform. In many instances, however, the disparity in height between the truck deck and the deck of platform is so great that cargo cannot easily be transferred to the platform despite the use of the rollers. These conditions occur for various reasons, including uneven ground, insufficient tire inflation on the truck, or equipment mismatch.
The present invention comprises a loader having a platform deck that includes an array of roller assemblies that are arranged in a plurality of groups. The groups include groups along the sides of the platform having longitudinal drive axes parallel to the loader axis, groups near the center of the platform having separate lateral drive axes that are perpendicular to the loader axis, and groups down the center of the platform having longitudinal drive axes parallel to the first mentioned group. The groups are independently motor-driven and rotatable about separate axes, so that different combinations of the groups can be used to achieve a desired movement of the cargo, including lateral and longitudinal movement and rotation. Groups that are not powered during a given load transfer operation are passive. Passive groups either provide reduced friction support or are not loaded during a given operation.
In accordance with another object of the invention, a loader constructed in accordance with the present invention includes load transfer cylindrical rollers on the sides and end of the deck that have much larger diameters than previously known rollers of this type. For example, it is preferred that the diameter of transfer rolls be at least eight, and more preferably at least ten, inches.